In recent years, various outdoor radio service systems have been able to be used, such as cellular phones, wireless LAN hotspot services, and WiMAX. In addition, in a broadcasting field, too, digital terrestrial television broadcasting has started. To effectively utilize a variety of such wireless services, it is important to improve antenna performance.
Meanwhile, terminals supporting the above-described plurality of services require wideband antennas. With the advance of miniaturization of terminals used for the above-described services, the sensitivity of antennas included in the terminals decreases.
An antenna that solves the aforementioned problems requires the following points:
(1) The antenna can support a variety of different bands, and secures a 25% or more frequency band in those bands or has wideband characteristics.
(2) The antenna is a wearable antenna that can be attached to clothing or a body. Even if the antenna is added to clothing, etc., the input impedance matching characteristics do not deteriorate and wideband characteristics can be obtained.
An antenna having the performance described in the above point (1) can use a plurality of services in a shared manner. An antenna having the performance described in the above point (2) is put on clothing and can thereby serve as a large antenna without becoming an obstacle. By allowing the antenna to serve as a large antenna, a sufficient received electric field or an antenna gain for communication can be obtained.
For a wideband antenna, there is a discone antenna such as that shown in FIG. 1. The antenna has wideband characteristics but has a three-dimensional configuration in which a disc 801 of a conductor and a cone 802 of a conductor are combined. A center coaxial conductor 804 of a coaxial cable 803 is connected to the disc 801, and an outer coaxial conductor 805 is connected to the cone 802.
For an antenna formed of a conductive fabric and mountable near a human body, there is a patch antenna made of a fabric such as that shown in FIG. 2. This antenna is disclosed in Non-Patent Literature 1. The patch antenna is formed of a patch 901 made of a conductive fabric; a ground 902, and an insulation fabric 903 serving as an insulator.
In addition, Patent Literature 1 describes a wideband antenna in which two radiating elements of a substantially right triangle shape are combined such that they are shifted from each other parallelly.